Field of the Invention
One or more embodiments of the present invention relate to a coated phosphor in which a phosphor is coated with a coating material and a method for producing the coated phosphor.
Background Art
Conventionally, it has been known that a sulfide phosphor is subjected to a hydrolysis reaction by water or the like to be changed to an oxide or a hydroxide, with the result that its characteristics, such as a light emitting intensity, a luminance or the like, are seriously lowered.
Patent Document 1 and Patent Document 2 have described methods in which by coating the surface of a phosphor with silicon dioxide by using a metal alkoxide through a sol-gel method, the phosphor is prevented from being made in contact with water so that the degradation of a phosphor due to hydrolysis is prevented and the characteristics of the phosphor (such as light-emitting intensity, luminance or the like) can be properly maintained.
However, even in the case when, by using methods described in Patent Document 1 and Patent Document 2, a moisture preventive property is achieved, the moisture preventive property is insufficient, and under a high-temperature, high-humidity condition, a sulfide phosphor may react with water to release a sulfur-based gas such as hydrogen sulfide or the like from the sulfide phosphor. When the sulfur-based gas is discharged, electrodes or the like are corroded in an electronic material system to cause degradation or the like of the conductivity.